What is the best combination for HDD . RAID 1 or RAID 5 Option 1-RAID1(OS) and RAID5(Ex database) Option 2-RAID5(OS) and RAID5(Ex database) Option 3e-RAID5(OS and exchange) I have 100plus mail boxes. What would be the in my case. Currently our mail server is free BSD . our head office and the branch network accessing mail via POP3 outlook. If I change to exchange 2007 our branch users will be able to access the head office exchange server without active directory authentication. our branch have their local active directory .

if only above 3 options are available, I will choose Option 1.Actually, RAID 0+1 is the best RAID solution to store Exchange database and logs in Exchange 2007 and also storing Database and Logs in different LUNs. But it depends again on your requirement no. of users, mail profile, mailbox size, recovery requirements etc. etc.You can use following calculator to arrive on recommended configuration.http://msexchangeteam.com/archive/2007/01/15/432207.aspxIf you implement Exchange 2007, branch users can access the mailbox but yes they will definately need active directory authentication. However, it is not must to install local active directory. For. e.g. you can use Outlook Anywhere.http://technet.microsoft.com/en-us/library/bb123513(EXCHG.80).aspxAlso, Exchange 2010 is there, you can also consider implementing 2010, as it will provide improved functionality & features.All the best.-V